Note: Descriptions are shown in the official language in which they were submitted.
POSITIVE DISPI.ACEMENT PUMPS
BAC~GROUND OF THE INVENTION
This invention relates to pumps and pumping methods.
It especially relates to pumps which are operated at high
pump speeds in pumping low viscosity liquids, especially in
large volumes.
As used herein, high speed operation of a pump means
operation at speeds of at least 500 revolutions per minute
(rpm), preferably at least 900 rpm, and most preferably at
least 1200 rpm. It is anticipated that pumps disclosed
herein can be operated at sustained speeds hetween about
1500 rpm and about 1900 rpm.
It is known to use positive displacement pumps, having
counter-rotating twin screws, for pumping higher viscosity
products, such as pastes, creams, oils and the like.
It is known to use pumps which are not generally
considered to be positive displacement pumps for pumping
low viscosity fluids, such as water at high speed and in
large volumes.
In the papermaking art, it is known to use fan pumps
for pumping two and three phase media which are part liquid
and part gas, for example foamed liquid containing 50 to ~0
percent air by volume, which optlonally include some solid
material. Foamed fiber furnishes containing solid cellulo-
sic fibers for use in papermaking processes are well known
as disclosed, for example, in United States Patent
4,443,297 to Cheshire et al, herein incorporated by
reference. Pumping of such multi-phase foam media has
presented a plurality of problems as the pump speed, the
volume of flow, and outlet pressure have been increased.
Using conventional fan pumps, the increase in flow volume
has not corresponded well with increase in speed of the pump
because of the compressibility of the foamed media.
Accordingly, in order to achieve efficient pumping at
higher volumes and higher pump speeds, applicants have
found it expedlent to use a positive displacement pump for
pumping such foamed media. Such pumps have conventionally
been used for pumping higher viscosity products, generally
2~$,~
product5 which provide some fluid lubricity between the
stationary pump casing and the moving impeller (e.g. screw).
An advantase of such positive displacement pumps is
that they generally create isolated batches of the media
being pumped, isolating the batches essentially at, or near,
the inlet pressure, whereby batches of foamed media are
susceptible to being pumped from the inlet to the outlet in
essentially predictable volume, wherein the volume pumped,
as measured at the pump inlet, is essentially linearly
related to the speed of operation of the pump.
Applicants have found that, when pumping the above
mentioned foamed media at e.g. 900 rpm, the pumping opera-
tion creates pressure pulses which are transmitted thro~gh
the outlet of the pump. Essentially, the fluid in a
isolated pumping cell is at a pressure below the outlet
pxessure of the pump. Upon reaching the outlet, the
pressure in the fluid at the outlet suddenly rushes into
the open cell and compresses the fluid in the cell. The
sudden rushing OI the fluid into the newly opened cell
causes a ra?id, temporary, pressure change at the pump
outlet. This pressure change is transmitted out of the
pump, throush the pump outlet, as a pressure pulse in the
fluid in the enclosed pressurized system downstream of the
pump .
While such pressure pulses are of little consequence in
operations which comprise only transfer of the media, where
the output of the pump is intimately connected with the
formation of the web in a papermaking process, such pressure
pulses directly a~~fect the uniformity of flow of furnish
onto the paper-ma~ing fabric, and accordingly, the unifor-
mity, in the machine direction, or the paper so made.
Applicants have also found that some conventionally-
produced screw type positive displacement pumps experience
excessive rates of wear when operated for sustalned periods
at their rated sDeed of 900 rpm for pumping the above
recited tkree phase media, containing about 1% to about 4%
by weight cellulose fiber. For example, a typical such
pump, having a designed clearance or 0.020 inch (0.5 mm.)
~ ~ ~ r~
between the rotati~g pumping screw and the stationary bore,
had a measured clearance of 0.040 inches (1.0 mm.) after
sustained operation ~or only three hours.
It is an object of this invention to provide improved
screw pumps which can withstand high speed operation over
extended periods of time with substantially reduced wear
between the stationary and the rotating members.
It is another object to provide means to measure the
wear of the pump parts without disassembling the moving
member from the stationary member.
It is a further object to provide means to monitor the
wear of the pump parts over time without disassembling the
moving member from the stationary member.
It is another object to provide a method o monitoring
the wear of the pum? parts without disassembling the moving
member from the sta~ionary member.
It is still another object to provide pumps which can
pump low viscosity --luids at hiyh speed operation with lower
amplitude pressure ?ulses.
- It is yet another object to provide pumps which can
pump low vlscosity fluids a~ high speed operation with lower
rates of change of ~ressure.
It is still another object to provide a method of
pumping low viscosity fluids at high speed operation with
lower amplitude pressure pulses.
It is a further object to provide a method of pumping
low viscosity fluids at high speed operation with lower
rates of changes of pressure.
It is yet another object to provide a method of
balancing a screw for a screw pump without increasing the
leakage between the higher pressure outlet end of the screw
and the lower pressure inlet end of the screw, at the loci
of removing material for achievement of balance, or other-
wise reducing the pumping capacity of the screw over a
typical 360 degree rotation of the screw; and without
significantly wea~ening the screw.
SUM~IARY OF THE DISCLOSURE
Certain of the objectives are achieved in a family of
positive displacement pumps, comprising an outer casing, and
first and second pumping screws. The outer casing comprises
an inlet, an outlet, and internal passage means adapted to
convey material between the inlet and the outlet. The
pumping screws have first portions contained in the passage
means. The passage means has an inner surface adjacent the
pumping screws, portions of the inner surface defining a
space therebetween, the space comprising a bore. Each
pumping screw has a minor circumference defined by a central
shaft, and a major circumference defined by at least one
screw flight. A second portion of each of the pumping screws
is contained in the bore over a length of the bore wherein
~he bore and the flisht are coextensive. The screw flight
extends radially and longitudinally about the shaft, and
outwardly from the shaft, to an outer surface of the flight,
at least a portion of the outer surface being defined in the
major circumference. Front and rear surfaces of the flight
extend between the shaft and the outer surface, and define a
thickness of the flight there-between. Each flight has a
height, as measured between the shaft and the outer surface.
The screw flights are secured to the respective shafts and
have inlet and outlet ends. Each screw fligh~ terminates at
the outlet end thereof.
Certain of the objectives are obtained in a family of
positive displacement pumps, also comprising an outer casing
and first and second pumping screws, the casing comprising
an inlet, an outlet, and the internal passage means. The
pumping screws have the same minor and major circumferences,
and the same general arrangements of the fli~hts on the
shafts. The passage means comprises the bore, having an
inner surface, and adapted to receive portions of the
pumping screws. The flights are similarly received in the
boxe with similar clearances. First and second bearings
mount each of the pumping screws to the casing at spaced
locations thereo.. The flights are disposed between the
bearings. The screws comprise one or more balancing holes
2 ~
in corresponding flights thereo~, tHe balancing holes being
disposed on surIaces of the flights, and being adapted to
reduce an~ tendency of the screws toward imbalance, the
balancing holes being disposed on, or below, surfaces such
that they will not materially reduce the pumping capacity
of the pump.
The balancing holes may be plugged with material
having a density less than the average density of the
respective ones of the flights. The holes are preferably
capped and ground such that the outer surface of the flight
is continuous and smooth over the holes.
Certain of the objectives are achieved in a more
generically ~efined screw pump comprising an outer casing
and a screw. The outer casing comprises an inlet, an
outlet, and inte~nal passage means adapted to convey
material between the inlet and the outlet. The pumping
screw has a minor circumference defined by a central shaft,
and a major circumference defined by at least one screw
flight. The screw flight extends radially and longitudi-
nally about the sh2-t, and outwardly from the shaft, to an
outer surface of the flight, at leas~ a portion of the outer
surface being defined in the major circumference. The
passage means comprises a bore adapted to receive at least a
portion of the pum2ing screw, the bore comprising an inner
surface. A irst portion of the flight is received in the
bore over a length of the bore wherein the bore and the
flight are coextensive. The clearance between the outer
surface of the flight and the inner surface of the bore is
sufficiently small as to promote efficient pumping of
material through the bore by the screw. A wear measurement
port extends through the outer casing, from an outer end
thereof on the outside surface of the pump to an inner end
thereo~ at the inner surface of the bore propinquant the
major circumference defined by the outer surface of the
screw, upon rotation of the screw. The wear measurement
port is positioned such that a portion of the outer surface
o, the flight can be disposed adjacent the inner end of the
~3~ ~3
port, whereby a measurement device can be manipulated in or
through the port, and the wear of the scr~w can thus be
measured.
The screw and the outer casing preferably include
indicators which indicate that angular position of the screw
at which the outer surface is disposed in measurement
position at the wear measurement port.
In preferred embodiments within this family, a proxim-
ity sensor is dis?osed in the wear measurement port, and
means for transmitting a signal generated ~y the proximity
sensor extends from ~he proximity sensor and the wear
measurement port, the wear measurement port being closed and
sealed sufficient for normal operation of the pump.
Certain of the objects or the invention are achieved in
a screw pump, pre-^erably a positive displacement pum?
wherein the flights comprise elongate hardened wear strips
as components of the outex surfaces of the flights, each
wear strip having a width corresponding in direction to the
corresponding width of the corresponding one of the outer
surfaces, less than 50% of the width of a given length
portion OI the outer surface being comprised of the wear
strip.
In some embodiments, a portion of the wear strip is
prererably overlain by the softer material comprising the
main body OL the corresponding one of the screws, the
overlying softer material being adapted to hold the wear
strip against movement out of ~he flight in a direction
perpendicular to the longitudinal axis of the screw both
before and after initial wear o~ the wear strip at a surface
thereof corresponding to the outer surface of the screw.
In some embodiments, the widths of the wear strips vary
along the lengths of the flights such that the width of a
given wear strip at a given locus is related to the poten-
tial amount of wearing contact at the l~cus between the
respective one of the outer surfaces and the bore. In
those embodiments where the width of the strip varies
according to location on the flight, the wider widLhs or the
wear strips can e~compass greater than 50~ of the width of
the outer surface at a given locus, up to 100~, especially
~J ~
adjacent the outlet end of the flight at loci where the
width of the flight is tapering toward the zero thickness at
the outlet end of the flight.
Certain objects of the invention are achieved in a
method of monitoring wear in a screw pump. The method
comprises the ste?s of selecting an appropriate screw pump
having a port therein suitable for receiving a wear measure-
ment device, manipulating a measuring device through the
port, and measuring the wear of the respective one of the
screws, using the measuring device as manipulated through
the port. In the p~mp so used, the port is positioned such
that a portion of the outer surface of the respective flight
can be disposed adjacent the inner end of the port, along a
lonsitudinal axis extending along the length of the port,
whereby a measuring device can be manipulated through the
port and the wear o_ the screw can thus be measured.
In some embodiments, the wear measurement port has a
plug in it, and the method comprises, between the steps of
selecting the pump and manipulating the measurlng tool
therethrough, the steps of operating the pump, stopping the
opera.ion of the ?um?, and removing the plug.
In a preferred embodiment, a preferred wear measure-
ment device is a proximity sensor, and the method comprises
emplacing the proximity sensor in the port, sealing the port
closed, operating the pump by turning the screws with the
proximity sensor so emplaced, and sensing dynamic changes of
proximity of the flight to the sensor.
Still others of the objects are achieved in a method of
balancing screws used in the pumps. The method of balanc-
ing the above described screw comprises the steps of
determining the locus and amount of imbalance of the screw;
and removing material from the flight, in correcting the
imbalance, along that portion of the flight which is between
the bore and the bearings.
Certain of the objects are achieved in methods of
controlling the amplitude and/or the rate of change or
pressure pulses in a low viscosity pumping operation,
wherein the viscosity is no greater than 5 centipoise, and
wherein a positive displacement screw pump, as desc_ibed
2~$~ ~J'~
above, is used, an~ is operated at high speed, whereby the
pum? has an operating inlet pressure and an operating outlet
pressure. The purn?ing cells between facing portions of the
front and rear surfaces of the flight have cross sections
defined between the major and minor circumferences.
Indi~idual batches of the material ~eing pumped are substan-
tially isolated, in the pumping cells, from both the outlet
pressure and the inlet pressure during traverse of the screw
by the batches between the inlet and the outlet. The
individual batches of material are sequentially opened to
the outlet pxessure during operation of the pump and the
associated pumping of the material.
The method of controlling the pressure pulses in the
last described o?eration comprises opening the cells to the
outlet ?ressure by creating an opening between a respective
cell ar.d the outlet, wherein the cross-section of the
opening is at least as great as the cross-section of the
cell, over a period of time greater than the time during
which, at the speed of operation of the pump, the flight
traverses an arc, as measured transverse to the sha-t,
wherein the cross-section oî the s?ace defined between the
arc at the major circumference and the shaft is ecual to the
cross-section of the corresponding pumping cell.
Pre_erably, the cells are opened over a period of time
at least two times, more preferably at least six times, in
some embodirnent preferably at least ten times, and up to at
least _ifteen times, as great as the time during which the
flight txaverse the arc.
$ ~
BRIEF D~SGRIPTION OF THE DRAWINGS
FIGURE 1 shows a front view of a pump of the invention
with portions cut away.
FIGURE 2 shows a transverse cross-section of a portion
of the pump, and is taken at 2-2 of FIGURE 1.
FIGURE 3 is a fragmentary cross-section showing an
alternative combination o~ bore and screw, to achieve
reduced pressure pulsation effect.
FIGURE 4 shows a fragmentary cross-section including a
dynamic control system adapted to reducing pressure pulsa-
tion by providing control apparatus for controlling the
amount of pressure lea~age, from the screw outlet area back
toward the screw inlet ends.
FIGUR~ S shows a cross-section of a balancing hole and
is taken at 5-5 of FIGURE 1.
FIGURES 6 and 7 show fragmentary cross-sections of the
screw and illustrate the wear strips on the screw.
FIGURr 8 is a view Oc the right side of the pump of
FIGURE 1~ showing wear strip variation with respect to
position on the screw.
~ 3
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
Turning now to FIGURES 1 to 4, a pump 10 has an outer
casing 12, including an inlet 14, an outlet 16, and internal
passages generally designated 18, traversing the casing 12
between inlet 14 and outlet 16. Internal passages 18
include a bore 20 adapted to receive therein a pair OL-
pumping screws 22 and 24. The cross-section of bore 20, and
thus the space defined therein, is defined at any given
point along its length by an inner surface 26. The bore 20
further comprises an outer surface 27, and a wall 29 between
inner and outer surfaces 26 and 27.
Pumping screws 22 and 24 comprise minor circumferences
defined by shafts 28 and 30 respectively. Each shaft has a
longitudinal axis 33 extending along the length thereof.
Screws 22, 24, further comprise major circumferences 31
defined by the outer surfaces 32, see Figure 6, of helical screw f1ights
34, 36, 38, and 40, at the maximum circumferences of those
flights. In the embodiments illustrated, each shaft has an
attached pair of flights disposed toward opposing ends
thereof.
Sturfing boxes 42 and 43 are attached to opposing ends
of outer casing 12 and contain stuffing seals 44 and 45.
The stuffing ~oxes 42 and 43 support screws 22 and 24 on
bearings 46, 48, 50, and 52, the seals 44 and 45 being
disposed between the bearings and the pumping chamber which
is generally defined by internal passages 18. The bearings
and seals can, of course, be reversed in position for use in
pumping material which is adapted to lubricate the bearings.
A gear box 54 is mounted to the right end of the right
stuffing box 43 and houses gears 56 and 58 which are
preferably integral parts of the respective screws 22, 24 as
illustrated. Gears 56, 58 are arranged with the teeth or
gear 56 meshed with those of gear 58 such that the rotation
of shaft 28, by a motor or other prime mover(not shown),
causes counter-rotation of the screws 22, 24 whereby one o
screws 22, 24 rotates clockwise and the other screw rotates
counter-clockwise.
~ 3
11
Each of the screw flights extends radially and lon-
gitudinally about the respective shaft, and extends out-
wardly from the shaft to the outer surface 32 of th~
respective shaft. Each flight comprises a front surface 6C
disposed toward outlet 16 and a rear surface 62 disposec
away from outlet 16, front and rear surfaces 60 and 6
defining the thickness of the respective fllght therebetweer
at any point along the length of the respective flight. At
any point along a given flight, the flight has a height "H"
as measured between the respective shaft 28 or 30 and the
respective outer surface 32.
Pumping call spaces 64 and 66 are defined betweer.
facing portions of the front and rear surfaces of respective
flights 34 and 38, between the shaft 28 and the outer
surfaces 32 of the flights 34 and 38. Pumping cell spaces
68 and 70 are defined between facing front and rear surfaces
of respective flights 36 and 40, between the shaft 30 and
the outer surfaces 32 of flights 36 and 40.
As seen by the combined teachings of FIGURES l, 2 and 4
the flights 34, 36, 38, and 40 of the screws 22, 24 are
meshed between shafts 28, 30, by the design and positioning
of the screws, such that the flights 34, 38 on screw 22
reach into the pumping cell spaces 68, 70 on screw 24,
essentially closing off the cell spaces 68, 70 between the
shafts Z8 and 30. Similarly flights 36, 40 on screw 24
reach into the pumping cell spaces 64, 66 on screw 22,
essentially closing off the cell spaces 64, 66 between
shafts 28 and 30. The thicknesses of the fliyhts and the
spacing of the corresponding front and rear surfaces (the
width "W" of the cell spaces) on the adjacent flights
cooperate such that the clearances between the flights at
the meshed screws are small enough that the flight OI one
screw serves as an effective closure of the cell spaces of
the opposing screw at the loci where the screws are meshed
between their shafts.
The clearances between the outer surfaces 32 of the
respective fLights and the bore 20 are small enough, and
comprise enoush length of bore 20, to promote efficient
pumping of a low viscosity material, such as water, a foamec
~ ~ ,;d ~
liquid containing, (e.g. 50~ to 80~ air by volume,) and the
same media when including papermaking fibers dispersed
therein. Typical clearances are between about 0~02 and
about 0.04 inch ~about 0.5 to about 1.0 mm.). The typical
seal clearance is normally effective over at least one turn
of each flight, thereby effectively isolating the inlet end
of the flight from the outlet pxessure at the outlet and of
the flight.
The closure of the pumpi.ng cell spaces 64, 66, 68, and
70 by the meshing of the screws between shafts 28 and 30
creates at least one, and preferably a plurality of isolated
and distinct pumping cells 72 at each flight on each screw.
Each pumping cell 72 is defined within a pumping cell space
(e.g. 64) between facing front and rear surface portions 60,
62 between the respective shaft (e.g. 28) and the ad~acent
inner surface 26 o~ the bore 20, about generally one turn of
the pumping cell space (e.g. 64) between consecutive
extensions of the opposing flight (e.~. 36) into the pumping
cell at the locus of meshing of the screws. Accordinsly,
each pumping cell extends approximately one turn (a bit
less) about the shaft between adjacent turns of the cor-
responding flight. The cell has a beginning and an end
where the screws are meshed. Accordingly, the pumping cell
is isolated from the inlet, from the outlet, and from the
other cells. Upon turning of the screw (e.g. 22) in the
pumping direction, the pumping cells are advanced along the-
screw toward the outlet 16 at the center of screw 22.
The portions 7 4 of the screws which are in internal
passages 18 comprise the portions between the seals 44 and
45. The portions 74 include first lengths over which the
screws and the bore are coextensive (i.nside bore 20) and
second lengths between bore 20 and the respective seals 44,
45 .
Each screw flight 34, 36, 38, 40 begins at an inlet end
76 disposed toward the respective stu~fing seal 44 or 45 and
ends at an outlet end 78 disposed toward outlet 16. Inlet
end 76 of the flights may, and preferably does, extend at
least part or the distance between bore 20 and seals 44, 45.
Outlet end 73 is preferably configured as in FIGURES 1 and
2 ~ 3 ~
13
2, to reduce the pressure pulses in the pumped fluid. The
clearance between the outer surface 32 of the flight and
the inner surface 26 of the bore may be increased to the
outlet end 78 or the fli~ht over a portion of the coexistent
length of the bore and the screw along the longitudinal axis
of the shaft of the respective screw.
The e~bodiment illustrated in FIGURES 1 and 2 shows an
increase in the clearance between the outer surface of the
flight, at outlet end 78, and the inner surface 26 of the
boxe, over a full turn of 360 degrees of the flight on the
sha't (FIGU~E 2~.
The progressive increase in the clearance between the
outer surface 32 of the flight and the inner surface 26 of
the bore represents a progressive (gradual) opening of the
pumping cell to the operating pressure at the outlet 16 of
the pump, whereby the pulsating effect of the opening of the
cell is spread over a longer period of ti~e than if the
height of the flight came ~o an end, from its full height
at the major circumference, over a shorter distance during
high speed operation of the p~mp, which can develop about 50
psi pressure dif e ence between the pump outlet and the pump
inlet even at the lower speed of 909 rpm when pumping paper
making furnishes based on water or foamed llquid as herein
disclosed.
The provision of the progressive increase in clearance
ls illustrated in FIGURES 1 and 2 as a progressive decrease
in height "~" or the screw flights at the outlet ends 78 of
the flights, the size of the bore 20 being kept constant.
FIGURE 3 illustrates another method of achieving the
increase in clearance, namely an increase in the cross-
section of bore 20 adjacent the outlet end of the flight,
while the height n~ of the flight is maintained constant to
outlet end 78, in accordance with the respective major
circumference 31, or is tapered in height ovPr a relatively
shorter distance.
Both changes may, of course, be made, whereby the
height of the flight is progressively reduced and the cross-
section of the bore is changed (increase or decrease) to
acco~modate the desired rate of change in the clearance.
14
At the higher speeds of operation contem~lated for the
pumps of this lnvention, any imbalance in the screws will be
evidenced by vi~ration and wear in the screws and bores or
the pump. Accordingly the screws are prererably balanced.
The balancing is accomplished by defining the angle of
imbalance (the radial angle about the shaft whereat the
screw is heavy) and removing an appropriate amount of
material from the flights, to reduce that imbalance, at the
appropriate radial angle, at locations, and in such ways,
that the ins'antaneous efficiency of the ongoing pumping
operation will not be reduced.
Preferr-d locations for removing materi~l are shown in
FIGURE 1. Hidden holes 82 are located at distances approxi-
mately 25~ (and respectively 75%) of the distance between
the bearings 46, 52, whereby they reduce the tendency of the
screw to set up a standing one-cycle sine wave vibration.
Holes 82 are generally made by removing the calculated
amount of material with a drill. As illustrated in FIGUR~
;, the holes 82 are preferably capped with a cap 84 which is
welded in place over the hole, after which the cap 8~ is
machined or ground flush so that it becomes an integral part
OL the outer surface 32 of the flight. Accordingly, the
balancing holes 82 do not penetrate outer surface 32, and
thus have no ef ~c~ on the ability of the outer surface 32
to create isol2ted pumping cells with appropriate control of
~-luid leakage between outer surface 32 and inner surface 26
o~ bore 20 The balancing holes can be plugged with material of lower
density than that of the flight in which they are made.
As seen in FIGURE 2, wear measurement ports 86 extend
through outer casing 12, from inner ends 88 thereof at inner
surface 26 to outer ends 90 thereof at the outside surface
of the pump. Ports 86 have longitudinal axes 87, and are
closed by re~ovable plugs 92 which maintain the seal of the
pump during normal pump operation. The simplest plug 92
(left side in ~IGURE 2) is typically threaded, and is
removed when the pump is out of service, whereupon a
measuring tool is manipulated through the port 86 and
against the outer sur.ace 3~ or the respective flight. For
such use, it is necessary ~hat the screw be positioned such
that the outer surface 32 is aligned wi~A the hole 86,
,, D3
between hole 86 and the shaft of the screw. Preferably the
shaft 28 and the outside of the gear box, or other appro-
priate stationary surface, are marked at matching locations
thereof, as at 94 on shaft 28, such that alignment of mark
94 on shaft 28 with the matching mark on the outside surface
or the gear box brings the outer surfaces 32 of the flights
into alignment with the wear measurement ports 86 which are
so used.
The port 86 indicated on the right side of FIGURE 2 is
closed by a plug 96 which lncludes a dynamic proximity
sensor 98, connected by signal carrier 100 (e.g. wire cable)
to a monitoring device 102. Plug 96 is in place in port 86
while the pump is in operation. Upon each rotation of the
respective screw, the outer surface 32 passes proximity
sensor 98 whereupon a discreet signal is sent to monitor
102, which provides for monitoring of the wear of the pump
while the pump is in operation.- An acceptable proximity
t-ansducer system, including proximity sensor 98 and monitor
102 is the 7200 Proximitor, available from Kaman Instrumen-
tation Cor?oration, Colorado Springs, Colorado.
With such constant input of information from the
proximity sensor, it is now possible to record the proximity
as sensed over a ?eriod of time, and thereby to detect
changes in the proximity, which indicate wear or imminent
failure of the pump before the even~ occurs, whereupon the
complex papermaking process (or other process) can be shut
down in an orderly manner, and indeed such maintenance,
repair, or rebuild can be efficiently planned.
Referring now to FIGURF 4, there is shown therein a
fluid pressure feedback control system comprising fluid
pressure receiving ports 104, pipes 106, valves 108,
manifold 110, pipe 112, and fluid sending port 116. Fluid
pressure receiving ports 104 are similar to wear measure-
ment ports 86 in that they extend through wall ~7 of bore 20
to the inner suxface 26 of the bore. Ports 104 are typi-
cally spaced such that any pluxality of fluid pressure
receiving ports 104 open into different pumping cells.
Ports 104 are connected by pipes 106, through valves 108 and
maniîold 110 to pipe 112 which is in fluid communication
16
with the high pressure portion 114 of bore 20, through rluid
pressure sending port 116. 3y manipulating valves 108,
fluid at ~he outlet pressure of the pump can be controllably
and adjustably red back into the pumping cells, as indicated
at pressure gauges 118, whereby the pressure dirferential
between the high pressure portion 114 and the next ooening
one of the cells can be reduced by building the pressure in
the cell before it is fully opened to the outlet pressure at
the outlet end of the flight.
Similarly, the higher pressure fluid, and thus the
fluid pxessure, can also be fed by way of manifold 110, and
the respective valve 108, to any or each of the pressure
receiving ports 104. The pressure in the respective pumping
cells (e.g. 64) can thus be controlled, and increased
progressively in a given cell as the fluid traverses the
length of the flight, such that the pressure change ex-
?erienced by the fluid in a cell when the cell opens at
outlet end 78 is controlled, and the pressure change upon
opening or the cell to the outlet pressure can be minimized
when desired. And as the pressure change at flight outlet
end 78 is reduced, the pressure pulses associated with that
pressure change are also reduced, whereby the vibration and
resonance caused, in the downstream piping, by such pressure
pulses, is reduced. Thus, the pressure feedback control
system ll9 illustrated in FIGURE 4 can be efective to
reduce the fluid stress, es?ecially the vibration and
resonance stress, on the pump and on the piping and other
apparatus which is subjected to the output pressure of the
pump downstream from the pump.
One pressure feedbac~ system ll9 is shown in FIGURE 4,
for controlling the pressure along flight 34, it being
unders~ood that a similar feedbac~ control system is used
for each flight in the pump (e.g. 36, 38, and 40).
The resonance, vibration, etc., in the operating system
or which the pump is a part, as set up by high speed
operation of ~he several components thereof, can be somewhat
accommodated by manipulating the valves 108 to change the
intensi~y and duration of pressure pulses produced by pU-~?
10 in order to provide a dynamic control c~pabili.y in the
2.~
dynamic vibration aIId resonance environment. Further, as
vibration and resonance change in the operating system (e.g.
in response to chan5es in pump speed), the control valves
can be manlpulate~ to provide the changed optimum amounts of
fluid and pressure feed-back.
While the pumps of this invention are designed to
operate wit~. a clezrance of e.g. 0.02 inches (0.5 mm.)
between the screws 22, 24 and the bore 20, wherein the
screws 22, 24 are supported by bearings 46, 48, 50, 52 near
opposing ends thereof, and whereby the screws should never
touch the inner sur.ace 26 of bore 20, in actual practlce,
such touchins does occur, in part due to vibration and
resonance. In addition, the pumps which applicants con-
template using in paper making processes are large, e.g.
major an~ minor circumferences of 50 inches (127 cm.) and
25 inches (63.5 cm.) respectively, and unsupported distances
between bearinss 46, 48 and bearings 50, 52, of over 10
feet (3.05m). A variety of forces apply bending moments on
screws 22, 24. For example, the mass of the material in
screws 22, 24 encourages a certain amount of sag, in
response to ~ravity, in the middles of the screws, midway
between the su?portins bearings, centering around the locus
of outlet 16. This sas contributes to eccentric rotation or
the screw. As the screws rotate, they set up resonance
vibrations that contribute to eccentricity of the rotation.
Also, as taught in ~nited States Patent 2,463,460, the
screws tend to shift toward the discharge opening, in a
direction transverse to the lengths of the shafts 28, 30,
when the pump is operated.
With such forces being applied to the screws 22, 24,
the screws do experience some contact between the outer
surfaces 32 of the flights and the inner surrace 26 of bore
20. The momentum of the impacting contact is, of course,
related to the mass of the respective screw and the velocity
of the respective movement. Accordingly, outer surface 32
is effectively hardened to reduce the wear of the screw.
The hardenings preferred for screws 22, 24 are illustrated
in FIGURES 6-8.
3 2 ~
18
In FIGURE 6, a groove 120 is cut along the middle of
outer surface 32 of the flight, and is filled with a wear
hard material 122 suc:~ as tungsten carbide or stellite. The
wear hard material 122 is mechanically locked in place,
against movement in a direction transverse to the longi-
tudinal axis of the shaft 22, by the overlying material at
wedge 128. Hard material 122 can be applied, as conven-
tional, with a plasma arc. However, inserting a pre-formed
strand of material 122 into a groove 120 is preferred,
followed by locking the hard mate~ial in place by modest
deformation of the surrounding material to secure the lock
at wedge 128.
Since subs.antially less than half of the thickness,
overall, of the outer sur~ace 32 of the flight is occupied
by the hard material 122, the cost and difficultly of finish
grinding outer sur~ace 32, to form a unitary and uniform
surface as shown, is commensurately reduced as compared to
finish grinding the surface after applying hardening
material over the entire width of outer surface 32. The
mechanical locking at wedge 128 enables the use of a less
e~?ensive pre-formed strip of hard material rather than the
conventional more ex?ensive hot melted spray application of
hard material 2s a' 43 in United States Patent 3,841,805.
Alternative loci and orientations of attachment are
shown in FIGURE 7, wherein the hard material 122 is shown at
the leading and trailing edges 126 and 12~ respectively of
the outer surface 32, and can be at either or both edges,
leading edge preferred. At leading edge 126, the wear hard
material 122 is mechanically locked in place, against
movement in directions both transverse to the longitudinal
axls of the shaft 22 and parallel to the longitudinal axis
OI the shaft, by the overlying material at wedge 128,
similar to the mechanical locking illustrated in FIGURE 6.
In FIGURE 6, approximately half of the hard material 122
will be worn away by the time the mechanical locks OI the
corresponding wedges 128 are worn away. Similarly, a
significant amount of material 122 will be worn away at
leading edge 126 before the mechanical locks of the respec-
tive wedges 128 are worn away there.
?~
19
r IGURE 8 illustrates varying the width of the hard
material 122 along the length of the flight, according to
the proba~le rate of wear at any given locus on the screw.
Since the greateSt moment arm in the screws is adjacent the
outlet, the probabilities for wear are greatest adjacent
outlet 16, and become rather progressively less when one
moves in the directions toward the supporting bearings.
Accordingly, at the outlet ends 78 of the flights 38, 40 the
entire outer surraces 32 thereat are surfaced with hard
material 122. As one progresses along flights 38, 40
toward their inlet ends, the fractions of the surfaces 32
which are occupied by the wear hard material 122 become
progressively smaller as shown in FIGURE 8.
As described above, the pumps of this invention are
improved by incor?oration of a variety of modifications,
each of which can be used alone, or in any combination with
the others. Preferably, all the improvements are incor-
porated into a given pump whereby the cumulative benefits
thereof are obtained. Such pumps are improved by introduc-
ing some of the fluid at the outlet pressure to an isolated
pumping cell ?rior to completely opening the cell to the
outlet ?ressure, as illustrated in FIGURES 1-4. They are
improved by balancing the screws as illustrated in FIGUR~S 1
and 5, by careful selection of the locus of the balancing
holes as illustrated FIGURE l, and by capping, and grinding
smooth the caps on the balancing holes as seen in FIGURrS l
and 5. They are improved by providing sensors and monitors
to sense and monitor screw wear. They are improved by
providing pressure feedback control system 119 which allows
dynamic control o- the pumping pressure in the isolated
pumping cells 72.
Typical materials contemplated to be pumped by pumps of
this invention are low viscosity fluids such as water and
compositions containing a substantial amount o~ water.
Other materials could, of course, be pumped. A preferred
material is a foamed fiber furnish for paper making as dis-
closed in United States Patent 4,443,297 Cheshire et al.
Suitable papermaking foamed fiber furnishes contain from
about ;0 to about 80 percent air by volume. The overall
2 ~ 2 ~
li¢uid medium contains about 200 to about 300 ppm surfac
tant, such as ~he sur~actant sold under the trade name A-OK
by Arco Chemicals, Inc. Papermaking fiber is dispersed in
the foam at ~ concentration up to about 2~ to about 3~ by
weight.
In the pumping operation, a prime mover such as an
electric motor~ is coupled with shaft 28 of screw 22 at the
right end of the pump (FIGURE 1). As the motor rotates
shaft 28, the entire screw 22, including flights 34 and 38,
rotates, and is supported for rotation in bearings 46,52, as
well as end bearing 130~ As screw ~2 rotates, engaged gears
56, 58 cause simultaneous rotation of shaft 24 in the
opposite direction. Each of the flights 34, 36, 38, 40, are
pitched such that the rotation of the respective screw
causes material, which is entrapped in pumping cells
defined by the flights of the respective screws, to be
advanced, in the res?ective pumping cells, toward the outlet
ends 78 of the respective flights, and accordingly, toward
the outlet 16 of the pump 10.
Material to be pumped (e.g. three phase foamed fiber
rurnish) enters the pump at inlet 14 and follows dive_gent
paths to opposing inlet ends 76 of the flights on opposing
ends of bore 20. As the screws turn, the material is drawn
into bore 20 by the turning screws. As the material enters
bore 20, individual units of the material are entrapped in
pumping cells 72, where they are isolated from the inlet,
from the outlet, and from each other. The isolation is, of
course, violated in small part by the ordinary lea~age
tolerated by the small clearances between the several
respective parts of the pump. Continued turning of the
screws causes advancement of the pumping cells, and accord-
ingly the liquid entrapped therein, toward the outlet ends
78 of the llight, and ul~imately out of the pump at outlet
16.
While the pumps of this invention have been described
with respect to pumping water and aqueous foamed liquid
dispersions at contemplated conditions, ~hey can clearly be
used with other pumpable materials and at other pumping
conditions.
